1. Field of the Invention
The present invention relates generally to ink jet printing apparatus, and more particularly relates to the fabrication of piezoelectrically operable ink jet printhead assemblies.
2. Description of Related Art
A piezoelectrically actuated ink jet printhead is a device used to selectively eject tiny ink droplets onto a print medium sheet operatively fed through a printer, in which the printhead is incorporated, to thereby form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has, within its body portion, a single internal array of horizontally spaced, mutually parallel ink receiving channels. These internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric wall portions of the printhead body (typically formed from a piezoceramic material referred to as "PZT") separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice.
A conventional method of fabricating an ink jet printhead of this type has been to provide a rectangular block of piezoceramic material, such as the previously mentioned PZT material, position a thin layer of metallic material on a side surface of the block, and then form a spaced series of parallel grooves through the metallic layer and into the underlying side of the piezoceramic block.
After these grooves are formed (using, for example a precision dicing saw) a covering block of piezoceramic material is appropriately secured to the outer side of a front portion of the metallic layer to thereby cover the open sides of front portions of the grooves and convert them to the interior body channels which will ultimately be supplied with ink. The open rear ends of the channels are appropriately sealed off, and the orifice plate is secured to the front end of the resulting printhead body over the open front ends of the channels.
Behind the covering block portion of the printhead body the spaced apart, parallel portions of the metallic layer are used as electrical leads for transmitting piezoelectric driving signals, from an appropriate controller device, to the interior piezoceramic side walls that laterally bound the ink-filled channels along their lengths to laterally deflect such side walls and thereby create the desired ink droplet discharge through the printhead orifice plate.
While this conventional ink jet printhead fabrication method, with its single array of internal body grooves, provides a precisely spaced multiplicity of interior ink channels and associated ink discharge orifices, there is, of course, a physical limit with respect to the total number of ink discharge orifices per inch that may be produced in a given printhead body using such method.
In cases where it is desired to increase the total number of ink discharge orifices per inch beyond this physical limit, for example to double the number of orifices per inch, it has heretofore been necessary to "stack" two printhead bodies against one another, thereby undesirably doubling both the overall size of the printhead body and the total number of components needed to fabricate it.
It can readily be seen that it would be highly desirable to provide a method of fabricating an ink jet printhead, of the general type described above, in which the discharge orifice density (i.e., the number of ink discharge orifices per inch) is doubled without correspondingly doubling the size of the printhead or the total number of components needed to fabricate it. It is accordingly an object of the present invention to provide such an ink jet printhead fabrication method.